While at Google, Sacca began investing in companies as an angel investor, investing his own money in startup companies or receiving equity in exchange for advising. He served as a professional advisor to companies for a variety of matters, including strategy, optimizing user experience, raising money, and selling a company. This included Auctomatic (sold to Live Current Media) and Omnisio (sold to Google/YouTube). His first angel investment was in Photobucket, which was then sold to News Corp in 2007. His second investment was in Twitter. Entrepreneur Evan Williams had started a microblogging service called Twttr in 2006, and asked Sacca if he wanted to invest. Sacca invested $25,000 and began using the service, registering in July 2006 as the 102nd user on the site. He related to Forbes that "I wasted months trying to get others to believe it could be a real business, not just a toy," before deciding "to just buy it all myself." Sacca took part in a $5 million financing round for Twitter in late 2007 and ultimately created four separate funds to surreptitiously buy as many Twitter shares as possible. Sacca left Google in December 2007 after he had fully vested and sought additional opportunities to work with early-stage companies.
Sacca has stated that a turning point in his angel investing was in 2007, when he moved to the town of Truckee in the mountains close to Lake Tahoe. Entrepreneurs including Travis Kalanick and Sacca would spend hours discussing ideas at the residence, and Sacca eventually bought the house next door to host various visiting entrepreneurs. When money began to run low Sacca raised a new fund with investors such as Brad Feld, Marissa Mayer, Eric Schmidt, and JPMorgan Chase's Digital Growth Fund.